The former West Brom manager attracted a lot of criticism for leaving out defender Ferdinand, who has been in fine form for Manchester United this season.
Although the 33-year-old has been struggling with a long-standing back problem, Hodgson confirmed his decision was based purely on footballing reasons.
"Any decision you make as an England national team manager is a difficult one," Hodgson told Sky Sports News.
"There's so many good players out there so every time you turn your back on someone and give someone else a chance, you're opening yourself up to criticism that that person would be every bit as good as the one you've chosen."
One player who has been selected for England in Poland and Ukraine, however, is Cahill, who was one of Chelsea's star men as they produced a magnificent rearguard action to repel Bayern Munich's attackers before eventually triumphing on penalties at the Allianz Arena.
Hodgson believes the former Bolton defender has a bright future ahead of him and hopes he can form a centre-half partnership with John Terry at Chelsea that could benefit England.
"Gary Cahill is a lot younger, he's got a good future ahead of him and if he can bed in to the Chelsea team alongside John Terry, it'll help the partnership if they find themselves together with England," Hodgson said.
"Having picked the England team, we'll have to see if they find themsezlves together or not."
Hodgson also attracted attention after speaking with England predecessor Fabio Capello on Saturday night in Munich.
He welcomed the Italian sharing some useful advice.
"Fabio and I have been friends for a long time," Hodgson added. "We've known each other for a long time, we've worked together in Italy - or worked against each other in Italy - so it's always nice to meet him again.
"And of course it's very interesting to meet him at the moment and to hear some of his opinions. He's been very helpful, very forthright and very generous with his time."